Mock localStorage with Jest for React testing

jest.config.js

module.exports = {
  testPathIgnorePatterns: ['<rootDir>/.next/', '<rootDir>/node_modules/'],
  setupFiles: ['./test-setup.js']
}

local-storage-mock.js

module.exports = class LocalStorage {
  constructor() {
    this.store = {};
  }

  getItem(key) {
    return this.store[key] || null;
  }

  setItem(key, value) {
    this.store[key] = value.toString();
  }

  removeItem(key) {
    delete this.store[key];
  }

  reset() {
    this.store = {};
  }
};

test-setup.js

const LocalStorage = require('./local-storage-mock');

global.localStorage = new LocalStorage();